The Clever Circuit That Doubles Bandwidth

Why It Matters

Hundreds of millions of new mobile devices and high-bandwidth applications are taxing wireless networks worldwide.

Under the hood: This benchtop prototype of a new radio doubles capacity on cellular or Wi-Fi frequencies by generating signals that cancel so-called “self-interference.”

A startup spun out of Stanford says it has solved an age-old problem in radio communications with a new circuit and algorithm that allow data to be sent and received on the same radio frequency—thus doubling wireless capacity, at least in theory.

The company, Kumu Networks, has demonstrated the feat in a prototype and says it has agreed to run trials of the technology with unspecified major wireless carriers early next year.

The underlying technology, known as full-duplex radio, tackles a problem known as “self-interference.” As radios send and receive signals, the ones they send are billions of times stronger than the ones they receive. Any attempt to receive data on any given frequency is thwarted by the fact that the radio’s receiver is also picking up its own outgoing signal.

For this reason, most radios—including the ones in your smartphone, the base stations serving them, and Wi-Fi routers—send information out on one frequency and receive on another, or use the same frequency but rapidly toggle back and forth. Because of this inefficiency, radios use more wireless spectrum than is necessary.

To solve this, Kumu built an extremely fast circuit that can predict, moment by moment, how much interference a radio’s transmitter is about to create, and then generates a compensatory signal to cancel it out. The circuit generates a new signal with each packet of data sent, making it possible to work even in mobile devices, where the process of canceling signals is more complex because the objects they bounce off are constantly changing. “This was considered impossible to do for the past 100 years,” says Sachin Katti, assistant professor of electrical engineering and computer science at Stanford, and Kumu’s chief executive and cofounder.

Other companies, including satellite modem maker Comtech, previously used self-cancellation to boost bandwidth on satellite communications. But the Stanford team is the first to demonstrate it in the radios used in networks such as LTE and Wi-Fi, which required cancelling signals that are five orders of magnitude stronger. (More details can be found in this paper.)

Jeff Reed, director of the wireless research center at Virginia Tech, says the new radio rig appears to be a major advance, but he’s awaiting real-world results. “If their claims are true, those are some very impressive numbers,” Reed says. “It requires very precise timing to pull this off.”

This full-duplex technology isn’t the only trick that can seemingly pull new wireless capacity out of thin air. New ways of encoding data stand the chance of making wireless networks as much as 10 times more efficient in some cases (see “A Bandwidth Breakthrough”). Various research efforts are honing new ultrafast sensing and switching tricks to change frequencies on the fly, thus making far better use of available spectrum (see “Frequency Hopping Radio Wastes Less Spectrum”). And emerging software tools allow rapid reconfiguration of wired and wireless networks, creating new efficiencies (see “TR10: Software-Defined Networking”). “A lot of the spectrum is massively underutilized, and this is one of the tools to throw in there to make better use of spectrum,” says Muriel Medard, a professor at MIT’s Research Laboratory of Electronics, and a leader in the field of network coding.

Kumu’s technology—even if it works perfectly—won’t provide a big benefit in all situations. In cases where most traffic is going in one direction—such as during a video download—full-duplex technology opens up capacity that you don’t actually need, like adding inbound lanes during evening outbound rush-hour traffic. Nonetheless, Katti sees benefits “on every wireless device in existence from cell phones and towers to Wi-Fi to Bluetooth and everything in between.” Kumu Networks has received $10 million from investors, including Khosla Ventures and New Enterprise Associates.